Conventionally, the detergents mainly containing chlorofluorocarbon solvents, such as 1,1,2-trichloro-1,2,2-trifluoroethane, and chlorine-based solvents, such as trichloroethylene, perchloroethylene, trichloroethane, and ethylene chloride, have been used for the above parts. However, chlorine-based solvents and chlorofluorocarbon solvents have problems such as toxicity to humans, environmental pollutions such as water and soil pollutions, global warming, and ozone layer depletion. As a result, the cleaning process using these solvents are now being replaced with the method using aqueous detergents. However, the cleaning process using aqueous detergents consumes more time and energy in the drying process when compared with those methods using the above solvents.
Recently, in view of solving the problems attributed to aqueous detergents in the drying process, various methods have been proposed. For example, it is generally known to use a hot-air dryer as a dryer, but this method requires a long drying time. Therefore, high-pressure air blowing and vacuum drying are used together in combination with the hot-air dryer to shorten the drying time. Examples of methods employing draining agents include those using solvents, such as 2-propanol, those using fluorocarbon solvents, such as perfluorocarbon, those using fluorine-containing surfactants thinly to be adsorbed to the surface of the parts to repel rinsing water, and those using nonionic surfactants.
However, the above methods have the following problems. The high-pressure air blowers and vacuum dryers as mentioned above need large-scaled apparatuses, thereby making them too costly. The method using solvents requires anti-explosion facilities, thereby making its handling and maintenance complicated. The method of using a fluorocarbon solvent is costly. The method of using a fluorine-containing surfactant is effective for cleaning flat plates, but its effectiveness becomes poor for cleaning an object having a complicated shape because of remaining waterdrops on the surface. The method using the fluorine-containing surfactant also has the problem that the surfactant remains on the surface of various parts after drying, thereby making it unsuitable to be used for objects which need post-treatments, such as painting. The method using nonionic surfactants is relatively effective for cleaning an object having a complicated shape, but the nonionic surfactants remaining on the surface of the cleaning object sometimes produce stains on the surface.